1. Field of the Invention:
The present invention relates, in general, to welding apparatus and, more specifically, to clamps for clamping parts or metal sheets together for welding.
2. Description of the Prior Art:
Welding is commonly employed as an assembly method for joining several metal parts or sheets together into an assembly. Various welding methods are available, such as arc and resistance spot welding.
Resistance spot welding is widely employed in vehicle assembly to join together several metal sheets or sub-assemblies into a larger assembly. Resistance spot welding utilizes a pair of electrodes which are positioned on opposite sides of the parts or metal sheets which are to be welded. The electrodes are brought together under high pressure to force the parts into contact at the area of weld between the electrode tips before a high electric current is passed through the tips creating a molten zone of metal which, after cooling, solidifies to a solid weld nugget joining the parts or sheets together.
Clamps of various types are employed to hold the parts together in position before and during such welding operations. Such clamps include a clamp member configured to the shape of one or more of the parts so as to engage the parts and hold them in a fixed position relative to other part(s). The clamp member is moved between unclamped and clamped positions by a variety of means including manually operated, over-center toggles and fluid operated cylinders.
While such clamps hold the parts together under pressure, the pressure is directed solely to prevent the parts from moving relative to each other. Such clamps function only as part positioning members with welding being performed adjacent to or in a location spaced from the portion of the clamp which engages the parts. Pressure at the weld site is not required in resistance spot welding to insure contact between the parts since the electrodes are brought together under pressure to urge the parts together and insure contact between the parts or metal sheets at the weld site.
Recently, laser welding has been developed which affords several advantages over other more conventional forms of welding. The sharp focusing of the laser beam allows a concentration of energy capable of providing faster welding with less heat being introduced into the surrounding portions of the parts. In laser welding, a beam of laser radiation is focused onto a weld site in a stack of metal sheets or metal thicknesses at a focal point within the lowermost sheet or part. This beam causes a molten zone of metal to be formed in the stack in a cone shape extending from the upper surface of the top most sheet to the focal point of the beam within the lowermost sheet in the metal stack. This molten zone, when cooled, solidifies to join the sheets together. The laser weld is generally formed in an elongated, thin line and a laser weld of approximately 3/4 inch in length has been found to be equivalent in strength to a single weld nugget formed by resistance spot welding.
However, for the laser weld to be properly formed, the metal sheets must be in continuous contact along the entire length of the laser weld. Any gaps between the metal sheets caused by mispositioning of the sheets, misformed parts or bent parts results in no weld or a weld having insufficient strength. Thus, it is necessary that the metal sheets be in continuous contact along the entire length of the laser weld. Previously devised clamps for resistance spot welding and other welding operations are inadequate at insuring such continuous contact since the clamp engages the parts at a location separate or apart from the weld site and does not force the parts together in a stack between the clamp and an underlying solid backup. Further, laser welding lacks the pressure of the welding electrodes in resistance spot welding operations which insures complete metal contact between the parts at the weld site.
Thus, it would be desirable to provide a clamp for laser welding operations which insures complete and continuous contact between the metal sheets or parts along the entire length of the laser weld site. It would also be desirable to provide a clamp for laser welding which can be configured in a variety of shapes to conform to any desired weld pattern or part shape. It would also be desirable to provide a clamp for laser welding which is usable with conventional clamp operating devices, such as manually operated toggles or fluid operated cylinders.